1. Field of the Invention
The present invention relates to methods for preventing or removing biofilm on a surface.
2. Description of the Related Art
Biofilms are biological films that develop and persist at the surfaces of biotic or abiotic objects in aqueous environments from the adsorption of microbial cells onto the solid surfaces. This adsorption can provide a competitive advantage for the microorganisms since they can reproduce, are accessible to a wider variety of nutrients and oxygen conditions, are not washed away, and are less sensitive to antimicrobial agents. The formation of the biofilm is also accompanied by the production of exo-polymeric materials (polysaccharides, polyuronic acids, alginates, glycoproteins, and proteins) which together with the cells form thick layers of differentiated structures separated by water-filled spaces. The resident microorganisms may be individual species of microbial cells or mixed communities of microbial cells, which may include aerobic and anaerobic bacteria, algae, protozoa, and fungi. Thus, the biofilm is a complex assembly of living microorganisms embedded in an organic structure composed of one or more matrix polymers which are secreted by the resident microorganisms.
Biofilms can develop into macroscopic structures several millimeters or centimeters in thickness and cover large surface areas. For non-living objects, these formations can play a role in restricting or entirely blocking flow in plumbing systems, decreasing heat transfer in heat exchangers, or causing pathogenic problems in municipal water supplies, food processing, medical devices (e.g., catheters, orthopedic devices, implants). Moreover, biofilms often decrease the life of materials through corrosive action mediated by the embedded microorganisms. This biological fouling is a serious economic problem in industrial water process systems, pulp and paper production processes, cooling water systems, injection wells for oil recovery, cooling towers, porous media (sand and soil), marine environments, and air conditioning systems, and any closed water recirculation system. Biofilms are also a severe problem in medical science and industry causing dental plaque, infections (Costerton et al., 1999, Science 284: 1318-1322), contaminated endoscopes and contact lenses, prosthetic device colonisation and biofilm formation on medical implants.
The removal or prevention of biofilm traditionally requires the use of dispersants, surfactants, detergents, enzyme formulations, anti-microbials, biocides, boil-out procedures, and/or corrosive chemicals, e.g., base. Procedures for using these measures are well known in the art. For example, removal of biofilm build-up in a paper machine in the pulp and paper industry traditionally requires a deposit control program including proper housekeeping to keep surfaces free of splashed stock, anti-microbial treatment of fresh water and additives, the use of biocides to reduce microbiological growth on the machine, and scheduled boil-outs to remove the deposits that do form.
Bacteria growing in biofilms are more resistant to antibiotics and disinfectants than planktonic cells and the resistance increases with the age of the biofilm. Bacterial biofilm also exhibits increased physical resistance towards desiccation, extreme temperatures or light. As mentioned, biofilm formation causes industrial, environmental and medical problems and the difficulties in cleaning and disinfection of bacterial biofilm with chemicals is a major concern in many industries. Furthermore, the trend towards milder disinfection and cleaning compositions may increase the insufficient cleaning of surfaces covered with biofilm.
The formation of a biofilm by Pseudomonas aeruginosa involves the production of at least two extracellular signals involved in cell-to cell communication (WO 98/58075). The two cell-to-cell signaling systems are the lasR-lasI and rhlR-rhiI (also called vsmR-vsmI) systems (Davies et al., 1998, Science 280: 295-298). The lasI gene directs the synthesis of a diffusible extracellular signal, N-(3-oxododecanoyl)-L-homoserine lactone. The lasRproduct is a transcriptional regulator that requires sufficient levels of N-(3-oxododecanoyl)-L-homoserine lactone to activate a number of virulence genes, including lasI, and the rhlR-rhlI system. The rhiI gene directs the synthesis of the extracellular signal, N-buytryl-L-homoserine lactone, which is required for activation of virulence genes and expression of the stationary-phase factor, RpoS, by the rhlR gene product. This type of gene regulation has been termed quorum sensing and response. Davies et al. have demonstrated that the lasR-lasI system is involved in the differentiation of biofilm formation. WO 98/58075 provides a method whereby cell-cell communication in bacteria via the lasR-lasI system is manipulated to control biofilm architecture and structural integrity.
It is an object of the present invention to provide improved methods for preventing or removing biofilm present on a surface.
The present invention relates to methods for preventing or removing biofilm on a surface, comprising contacting the surface with an effective amount of a composition comprising one or more acylases and a carrier to degrade a lactone produced by one or more microorganisms, wherein the degradation of the lactone prevents or removes the biofilm.